Journal Club 2015 | Tanabe Photonic Structure Group

Journal Club

By fiscal year (April-December)

Fiscal Year 2015

Presentation Details:

Non-polarizable dielectric multilayer reflectors are important optical devices and have numerous applications in optical fibers, dielectric waveguides, and light-emitting diodes. In this study, we report the results of our analysis of biological unpolarized optical mechanisms in broadband guanine-cytoplasmic "silvery" multilayer reflectors of three fish species. Two types of birefringent guanine crystals are present in the silvery subcutaneous layers of those fish, one with the optical axis parallel to the long axis of the crystal and the other with the optical axis perpendicular to the crystal plane. Because of the different Brewster angles at each interface, these arrangements cancel the polarization of the reflections. The reflection mechanism in these fish differs from existing non-polarized mirror designs in the important respect that there is no refractive index difference between the low refractive index layer of the reflector and the external environment. This mechanism could be easily manufactured and used in artificial optical devices.

Presentation Details:

Laser microfabrication by two-photon absorption processing is one of the most advanced technologies in recent years, but there have not been many examples of evaluation of the fabricated products, and the technology has not yet reached the stage of research and practical use. In this study, we fabricated small spring structures made of PMMA polymer wires with diameters of several hundred nm by two-photon absorption processing, and evaluated whether the spring structures behaved in the same way as general springs from various viewpoints.

Presentation Details:

In this paper, we fabricated and characterized an optical modulator combining graphene and plasmons. By employing a modulation method via plasmons, which have a higher interaction with graphene than with light, and by using a waveguide structure with a higher interaction, a modulation depth of over 0.03 dB μm^-1 is achieved in an area of only 10 μm^-2. This is comparable to the performance of conventional silicon-based optical modulators, but smaller and more integrated, and is expected to play an important role in future optical communications.

Presentation Details:

The use of electromagnetic waves in the 0.1 to 1.0 THz range as a carrier wave for free-space wireless signals has been considered, but multiplexing terahertz signals has been a problem. In this study, we report on the demonstration of frequency multiplexing in a bandwidth of more than one octave using antennas based on parallel metal plate waveguides.

Presentation Details:

Optical tweezers have been widely studied for applications such as cell manipulation, fluid dynamics, and microrobotics, but it has been considered difficult to trap large particles with the Gaussian-shaped beams that are mainly used. In contrast, we propose a method (ENTRAPS) to increase the particle trapping force by simply manipulating the phase pattern of the incident beam, and report that we have actually observed an improvement of more than one order of magnitude in our experiments.

Presentation Details:

One of the most important nonlinear processes in optical fibers is four-wave mixing due to the intensity dependence of the refractive index. In this paper, we report a new nonlinear self-action effect, i.e., self-parametric amplification, in which the narrowing of the optical spectrum in a normal-dispersion fiber leads to a very stable propagation with a unique spectral distribution. The narrowing of the spectrum is due to inverse four-wave mixing, similar to effective parametric amplification in the middle of the spectrum due to energy transfer from the tail. Self-parametric amplification and stable nonlinear spectral propagation with observed random time waveforms are applicable to optical communications and high-power fiber lasers exhibiting nonlinear intracavity dynamics.

Presentation Details:

Today's increasing amount of data communication in data centers and computers requires transmission lines with high bandwidth and throughput. In this paper, we present an optical polymer waveguide that can be fabricated on a conventional CMOS electrical circuit board. This enables the incorporation of optical transmission lines between chips, whereas optical fibers have been used only for in/output from the board end.

Presentation Details:

Color discrimination requires a narrow linewidth spectral response, but current systems use a combination of broadband photodiodes and optical filters, which complicates the structure and limits the quality of color sensing.
This paper reports a method to realize filterless narrow-band photodiodes by adjusting the spectral response.
Since this research uses perovskite single crystals and is in the same field as the paper introduced by Tamaki on October 16, the presentation will include the difference in performance.

Presentation Details:

The need for non-volatile all-optical memory, which is essential for realizing all-optical signal processing, is currently increasing. In this study, we investigate the optical properties of a material that differs between the crystalline and amorphous states, Ge2Sb.2Te5(GST)-based nonvolatile all-optical memory. The transmittance of the GST-based all-optical memory device was significantly changed by guiding a write pulse through the GST-added waveguide, and by guiding a read pulse through the same waveguide. The device can be operated at room temperature, can be used repeatedly, and can store data for more than three months.

Presentation Details:

Trihalogenated organolead perovskites are attracting attention as a new electronic device material because of their low cost and the ability to prepare and fabricate band gaps in a solution process. In this paper, we report on a single-crystal perovskite photodetector that exhibits a very narrow spectral response with a full width at half maximum of 20 nm. This very narrow spectral sensitivity can be explained by surface charge recombination and is expected to be applied to all fields of sensing and imaging where the influence of noise should be suppressed.

Presentation Details:

We have successfully generated and mode-locked an optical Kerr comb in the normal dispersion region by using intermodal interaction. The spectra and time waveforms were measured, and it was confirmed that dark pulses were generated. If mode-locking can be achieved in the normal dispersion region, for example in the visible band where material dispersion is large, the resonator design can be more flexible, which may lead to further broadening of the comb's bandwidth.

Presentation Details:

In this paper, we show that chiral photonic circuits composed of quantum dots and asymmetric photonic structures can realize on-chip asymmetric photonic devices.
Because such devices are asymmetric in terms of the direction of photon passage, they can be applied to single-photon diodes, and can also be important components of single-photon transistors and deterministic quantum gates.

Presentation Details:

Optical microcavities, which confine light within a tiny resonator, are widely used for various applications ranging from the realization of lasers and nonlinear devices to biochemical and optomechanical sensing. In this work, we demonstrate in vitro various optical functions, such as laser oscillation, using microcavities and appropriate optical gain materials inside living cells. We are investigating two types of microcavities, soft and hard, that utilize the whispering gallery mode. Intracellular laser operation has been achieved with soft droplets formed by injecting oil droplets and soft droplets formed by using natural lipid droplets. The laser spectrum of the oil droplet microlaser illustrated the internal cytoplasmic stress (about 500 pN/μm^2 ) and its dynamic variation, with a sensitivity of 20 pN/μm^2 (20 Pa). Another hard type, utilizing the whispering gallery mode within phagocytosed polystyrene beads of various sizes, can easily tag thousands of cells individually, and in principle can be multiplexed with various dyes to tag even more cells.

Presentation Details:

In order to reduce the spread angle of light, we investigated and fabricated a structure in which a microscopic lens and a waveguide are integrated on a chip using photolithography and reflow, and evaluated its optical performance. As a result, the fabricated waveguide has a significantly improved spread angle of 1.85°, compared to a typical waveguide of 12.4°. Although some previous studies have used lenses and waveguides to reduce the spread angle, the method used in this study has the advantage that it can be used for fabrication of waveguides other than SiON waveguides.

Presentation Details:

Using silicon photonics technology, we have developed an RF signal generator capable of outputting 50 GHz signals, which can be arbitrarily tuned with eight micro rings to achieve π-phase shift and amplitude modulation. The RF signal generator can be tuned to any of eight microrings, enabling π-phase shift and amplitude modulation.

Presentation Details:

Shows 1 × 2 switching for mode-multiplexed and wavelength-multiplexed transmission using single and multimode waveguides integrated on a photonic chip. The switch exhibits a power penalty of less than 1.4 dB with a BER of less than 10^-9 when transmitting 10 Gb/s data separately. When transmitted simultaneously, the additional power penalty was less than 2.4 dB.

Presentation Details:

Nanowire lasers have the same oscillation principle as conventional semiconductors, but they are expected to be the next-generation semiconductor technology, such as laser oscillation at 1/10,000 of the volume of conventional semiconductors. In this study, we fabricated nanowire lasers with quantum dots in the active layer and achieved room-temperature laser oscillation.

Presentation Details:

By utilizing the interference between two resonators with different FSRs due to the Vernier effect, it is possible to shift the interference fringe peak by one channel even with a small change in FSR, and to limit the modes to be excited. However, in the conventional method, the resonance frequency splits due to the coupling of the two resonators.
In this study, we propose a system in which two ring resonators are indirectly coupled by a waveguide, and the phase state inside the resonators (imaginary part of the resonance frequency) splits without splitting the resonance frequency. By performing laser oscillation in the split state, called the dark state, the same effect as the conventional Vernier effect can be expected, and it is described in this paper that the resonance frequency does not split.

Presentation Details:

Metamaterials are attracting attention as new optical devices because they exhibit properties that are impossible for naturally occurring materials, such as a negative refractive index. However, because of the large propagation loss in the three-dimensional structure, metamaterials with a two-dimensional structure called hyperbolic metasurface have been studied. In this article, we will introduce the unique properties and behavior of plasmon propagation in the visible light band using hyperbolic metasurface.

Presentation Details:

While there has been much technical research on single-mode fibers, there has been little research, especially experiments, on the complex nonlinear phenomena that occur in multimode fibers. In this study, we experimentally demonstrated that various nonlinear phenomena can be controlled by spatially varying the pulse input conditions for multimode fibers.

Presentation Details:

The current challenge for practical quantum cryptography communication is to create secure and scalable quantum networks. One solution to this problem is the introduction of a measurement device-independent protocol, which enables long-distance key delivery, but suffers from a low key rate. In this paper, we show both theoretically and experimentally that this problem can be solved by using a continuous variable system, and we succeeded in obtaining a key rate three orders of magnitude higher than that currently achieved.

Presentation Details:

We predict the existence of flat-peaked dissipative solitons, or platicons, due to normal dispersion in microcavities. we describe how to generate platicons from cw excitation light, and suggest that their persistence may be strongly affected by detuning. by the Lugiato-Lefever equation. We argue that the discrete energy spectrum of dark solitons can be converted into a quasi-continuous spectrum of platycons. Similar structures can also be produced by phase- and amplitude-modulated excitation light, or by fixing the laser incidence.

Presentation Details:

In this paper, we propose a novel ultra-compact multiplexer based on a dielectric-loaded surface plasmon polariton waveguide (DLSPPW), which is a combination of Bragg grading and directional coupling. The fabricated multiplexer is 20 μm in length, and its ability to separate light in telecommunication wavelength bands with wavelengths 70 nm apart is demonstrated by simulation and experiment.

Presentation Details:

We have realized an optical isolator with a small element area, which is indispensable for realizing optical integrated circuits. The Fano spectrum generated from a photonic crystal with asymmetric structure was used to realize the device. The optical isolator operates at 10 Gbps and consumes only 4.5 fJ/bit.

Presentation Details:

Optical frequency combs are used for optical frequency measurement and spectroscopy due to their accuracy and coherence. In spectroscopy, optical frequency comb pulses with energy at the microJoule level are generated by a combination of total repetition rate amplification and an excitation resonator. In this paper, we report a spectroscopy method that selectively makes two pulses with millijoule-level energy. This spectroscopy is as accurate as conventional methods, and in some cases up to 30 times more accurate.

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What is Journal Club?
This is an open lecture series held in Tanabe Photonic Structures Laboratory. Students who are graduate students or above will survey papers related to optics and related technologies such as photonics, materials, bioscience, etc., and explain them in an easy-to-understand manner.

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Attendance is free, regardless of whether you are inside or outside of the university. The seminar will be held periodically, so if you are interested in any of the topics, please feel free to attend. No notice is required to attend, but we will prepare materials if you contact us in advance.

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